During the past year methods have been developed for the purification of plasma membranes of adrenal medullary cells. In the coming year the membranes will be characterized more fully with respect to their enzyme profiles with special attention to protein phosphokinases and protein phosphatases and their possible role in stimulus-secretion coupling. Additional studies are concerned with the identity of the soluble and membrane-bound form of dopamine beta-hydroxylase present in chromaffin vesicles. The membrane-bound and soluble forms of the enzyme have been purified and studies on the physical, chemical and immunological properties of each of the enzymes will be carried out to determine whether there is any intrinsic differences between the enzymes which can account for their distribution in the soluble matrix and insoluble membrance of the chromaffin vesicle. BIBLIOGRAPHIC REFERENCES: Ledbetter, F. H., and N. Kirshner, Studies of Chick Adrenal Medulla in Organ Culture, Biochem. Pharmacol., 24, 967-974 (1975). Muller, T. W., and N. Kirshner, ATPase and Phosphatidylinositol Kinase Activities of Adrenal Chromaffin Vesicles, J. Neurochem., 24, 1155-1161, (1975).